Battalion support

[Vesku]

Without any further research I'd imagine that German infantry battalion would have pioneer company, mg company, ATgun platoon, few Stugs, various number of Stukas and artillery. For a vital mission increase airsupport and artillery ... probably few Stugs too.

For Brits ... anything. Usually for infantry division it's motorized infantry, ATguns, mgs, engineers, ... what a regiment has in reserve. If there is armoured units nearby they would probably be the first to be called for help (and they were always the favorite unit to be had in reserve but infantry might not have many tanks in use) but any unit that is near enough would be sent to stopping a river crossing if that is a vital point in defense, cooks, clerks, etc.

You could try figuring out which divisions would be where and what they have kept for their reserve, having a big picture figured out would answer your question. If this is for your "What if Germans had executed Seelion" then you have free hands, you can always say that Brits had tank division in reserve just where Germans attacked so 100 Cruisers is just what answered the call for help :)